The invention relates to planetary type, fixed ratio traction roller transmissions in which the contact forces applied to the traction surfaces of the transmission for the transmission of motion are dependent on the torque transmitted through the transmission.
Basic traction roller transmissions are described, for example, by Harold A. Rothbart in "Mechanical Design and Systems" Handbook, pages 14`-8 and 14-9, McGraw-Hill, New York, 1964. In the relatively simple arrangements of FIGS. 14.6 and 14.7 wherein the outer rings of planetary-type transmissions are slightly undersized to compress the roller arrangements therein, the surface pressure on the traction surfaces is always the same, that is, it is always at the highest value even if only a small torque is transmitted through the transmission. As a result, wear and losses are always relatively high. In the arrangements shown on page 14-8 of said handbook, means are provided for engaging the traction surfaces with each other with forces which are dependent on the torque transmitted through the transmission.
It has been proposed to provide expandable sun roller structures provided with Belleville rings which, when axially compressed by torque-operated axial cams, were flattened to thereby grow radially and force the traction rollers into firm engagement with the traction ring (U.S. Ser. No. 281,983 assigned to the assignee of the present invention).
In another arrangement (descibed in U.S. Ser. No. 422,533, which is also assigned to the assignee of the present invention), a tapered ball screw structure is so associated with the sun roller or the traction ring that a torque transmitted through the transmission causes the tapered ball screw structure to expand radially for forcing the planetary traction rollers into firm engagement with the traction ring and the sun roller. However, while such an arrangement is quite simple, problems have arisen which limit the application of such transmissions. Especially, the transmission of larger torques is problematic as, in order to expand or compress the traction surface ring, the ball wedging angle must be relatively small so that the ring will remain locked under tension when the torque is reduced, especially if some torque is still applied.